This system is the work of our research assistant Jim Van Verth. It is designed to support refinement of molecular models. The goal is the near-real-time construction of 3D contour maps from x-ray crystallographic data to represent electron density distributions in protein crystals. This system will enable a user to change his model of a protein structure and observe immediately the effect of his change on various hybrid maps which are based on both the current model and crystallographic data. Among many improvements added over the past year, the system now handles the crystal space groups most commonly found for proteins and is extendible to all space groups. The model modifications available to the user have been extended as well. In addition to translations, Mr. Van Verth has added facilities for rotating molecular fragments either freely in space or constrained to rotated about the axis of a chemical bond. The system performance has been substantially improved. The system also supplements the display of maps and models in real space with the simultaneous display of the underlying structure factors in a second window. The project name, CORWIN, derives from "coupled reciprocal windows" and reflects this system feature that enables it to represent crystallographic data in both the real-space and frequency domains. Each structure factor is represented by a spot or a vector located at the hkl indices of the factor. The sizes of these spots or the brightness of the vectors represent the magnitudes of the structure factors. Their colors (and the directions of the vectors) represent the phase angles. We have begun developing a community of users both academic and commercial, and we are currently installing copies of the system in the departments of biochemistry both on our campus and at Duke University. During the past year we have begun a collaboration with Dr. Charles Carter of the Biochemistry Department on our campus that is described as the next subproject.